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envelope-from=drew.adams@oracle.com; helo=mx0b-00069f02.pphosted.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Users list for the GNU Emacs text editor List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Original-Sender: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Xref: news.gmane.io gmane.emacs.help:142440 Archived-At: > In Haskell you can't change variable bindings like in Lisp. You > program in a completely different style. Read an introduction into > Haskell if you are interested, then you'll understand the reaction. Yes - _completely_ different style, behavior, and meaning. This isn't specific to Haskell. But sure, that's a good example of a popular programming language that's _purely_ functional. (We should just say "functional", but that term has come to encompass even languages such as Lisp, and it pretty much just means languages that emphasize expression evaluation, with nesting and return values.) Languages that are purely functional (or purely logic(al)) use variables only in the _math_ sense: the value of a variable doesn't "vary". Variables aren't memory locations that are assigned values (more than once). In a given definitional context a variable has the same value everywhere. Same thing for function names. That, however, with the proviso that at the _top_ level such languages typically _do_ treat function names, and sometimes variable names, dynamically, i.e., as dynamic variables - variables in the traditional programming (assignment) sense: memory locations to be filled and refilled. E.g., you can redefine a function. There's no `let' at the top level, within which everything is defined. Note that Lisp - even "pure" lisp: only lexically scoped etc. - isn't a purely functional language. The mere presence of `quote' makes it referentially opaque. And even applicative evaluation order is a problem - not what you want in a useful functional language, in general. Lisp isn't lambda calculus or combinatory logic. And it doesn't pretend to be. Its impurity isn't shamefaced. ;-) Lisp is, well, loosey-goosey.